This invention relates to a method of unplugging fluidized solids transfer conduits. More particularly, it provides a method of readily re-fluidizing compacted solids plug which occasionally form in such conduits as a result of episodic flow or pressure disruptions.
The use of fluidization as a technique for contacting gases with solids, or for conveying solids, is widely practiced. See "Fluidization," in Kirk-Othmer's "Encyclopedia of Chemical Technology," Second Edition, Vol. 9, pp. 398 et seq. The various advantages of the technique are well known and widely availed of.
In chemical processing plants using fluidization, either as a contact technique or simply for solids transfer, a particularly aggravating situation occasionally occurs. The solids, as a powder or as granular materials, are typically suspended in a fluidizing gas stream and then conveyed through elongated transfer pipes or conduits. The solids flow, however is vulnerable to occasional disruptions in pressure, flow rate, solids concentration, or the like. When this occurs, the solids de-fluidize, and form a flow-obstructing, relatively compact, solid plug in the pipe or conduit. Because of the high solids content of the fluidized stream, the plug rapidly fills a substantial portion of the conduit, making it impervious to further solids flow, and, at times, to further gas flow.
When a pipe or conduit of this type becomes plugged, unplugging is more than merely troublesome. Sometimes it is necessary to disconnect the transfer conduit entirely, disassemble it into relatively short sections, and clean out each section separately. Alternatively, proposals have been made for having gas pressure taps every few score feet or so along the conduit, closing off the conduit inlet end, and sequentially blasting out solids by injecting gas from tap to tap, beginning near the outlet end.
Neither technique has been found acceptable. Both are time consuming, troublesome, not always effective, environmentally undesirable, or even hazardous. When, as is often the case, the solids are catalytically active, contact with air, moisture, or the like may inactivate the catalyst. In some processes, the solids are pyrophoric, and therefore combustible. Moreover, the lengthy time delays necessary to unplug the transfer lines, with concurrent termination of all flow during the unplugging period, can result in major plant shutdowns.
An especially serious situation occurs in catalytic processes where the catalyst is prepared at a location remote from the reactor. Here the transfer conduit may be several hundred or even several thousand feet in length, and of relatively small diameter, e.g., one inch pipe. Unplugging a one inch pipe several thousand feet long, which may include bends, may consume many hours or even days. Since the catalyst must be supplied to the reactor continuously, a plugged transfer line, to all intents and purposes, means a shut-down in the processing reactor.
Accordingly, an object of the invention is to provide a method for unplugging the elongated transfer pipes or conduits used in conveying fluidized powder or granular solid from a high pressure zone or area to a relatively lower pressure zone, which method is economical to install, convenient to use, and remarkably rapid and effective to operate.